You have the ability to build things properly so you should be ok especially as you have experience of welding slip rings. The duty is similar and if you can get things to survive for welding you should be ok.

You need good thick rings running concentric with reasonable bearings, the brushes need to be low resistance grade ( copper/graphite or similar) and they need good pressure ( higher than machine rings that rotate continuously). The best type of brush holders seem to be the ones where the brushes are fixed to the arms and spring loaded against the ring. Holders with brushes sliding in boxes are not well suited to non rotational applications with reversal of direction.

Try to use 2 brushes per ring and you will need good weather protection, they will fail without it. Failure usually starts as a poor contact due to corrosion of part of the ring in a wind direction where the thing rarely sits. This starts arcing and the destruction is cumulative with the  ring going out of round. You will no doubt have found the same trouble with welding turntables.

For normal machine applications oil is a disaster and must be avoided at all costs. For wind turbines there may be some case for a thin film of lubricant to act as a corrosion inhibitor but contact pressure must be high enough or you start a spark erosion process.

A hollow shaft with wires passing through may avoid the need for rings but they can be done satisfactorily. For the average person with limited facilities they are best avoided.